Role Of Stem Cell Division Modes During Cerebellar Development

Background: Asymmetrical and symmetrical divisions of neural stem cells play an important role during neural development,neural regeneration and tumorigenesis.In C.elegans,Drosophila and mammalian neural epithelia,such as brain,the regulation of symmetrical and asymmetrical divisions of neural stem cells have been well studied,but their role remains unknown in mammalian cerebellum.In addition,there is still no research to clarify the role of cerebellar granule precursor cell division modes in the early stage of the medulloblastoma development.In this paper,we use time-lapse recording monitoring and cell division axis labeling techniques to study the cell division modes in cerebellum neurogenesis and the early stage of medulloblastoma development.Objects:(1)To elucidate the cell division modes of cerebellar granule precursors in vitro and in vivo.(2)Using the cerebellar tumor mouse model to investigate the effect of Patched mutation on cerebellar granule cells division mode.(3)By analyzing the cell division axis change to explore the cellular mechanism of SHH signaling pathway on the regulation of precursor cell division modes.Materials and Methods:(1)In chapter 1,we analyzed the expression patterns of cerebellar granule progenitor cells marker Math1 and only neural differentiation marker Doublecortin in normal mice.(2)In chapter 2,we used the Math1-GFP;Dcx-DsRed double reporter mouse strain to study GNPs division modes in vitro and in vivo.(3)In chapter 3,we used the cerebellar tumor model Math1-GFP;Dcx-DsRed;Patched+/-trangenic mice to analyze the division modes of cerebellar granule cells after SHH signal activation.(4)In chapter 4,we used motosis marker PH3 to observe the change of granule cell division angle in wild type and Patched mutant mice and investigate the mechanism of the activation of SHH signaling pathway in the regulation of cell division.Results:(1)We observed that the precursor cells expressing green fluorescence(Math1-GFP)in the EGL,while on the bottom of EGL,a few differentiated DCX positive granule cells were found.(2)We found that cerebellar granule cells can undergo symmetrical and asymmetric division in vitro and in vivo.(3)In the early stage of the cerebellar tumor development,we visualized that the non-terminal symmetric division of granule cells significantly increased and blocked the normal differentiation of precursor cells.(4)By analyzing the change of precursor cell division axis,we demonstrated that the horizental division of cerebellar granule cells was significantly increased in Patched mutant mice,while SHH signal pathway was activated.Conclusion: Overall,by studying cell division patterns of the cerebellar granule cells,we found that during normal cerebellum neurogenesis,the pregenitors expand stem cell number by non-terminal symmetric division and produce differentiated granule cell through asymmetric division and terminal symmetric division.After activation of SHH signal pathway,the asymmetric division and terminal symmetric division decreased,while the non-terminal symmetric division increased.This finding clearly elucidated the mechanisms of hedgehog sonic signaling pathway in regulation of granular pregenitor cell division and may provide a basis for clinical diagnosis and treatment.